The present invention relates to a process and apparatus for controlling the concentration of solid particles suspended in a liquid.
An adequate control of the concentration of solid particles in suspension in a liquid is particularly necessary in connection with electrical discharge machining of an electrode workpiece by means of an electrode tool, with a machining fluid flowing between the electrodes. Solid particles in the machining fluid, whether they are a by-product of the electrical discharge machining or from the dust suspended in the ambient, have a great influence upon the triggering of the electrical discharges. It is known that electrical discharge machining becomes more effective if the concentration of solid particles in the machining fluid reaches a predetermined rate. It is therefore important to control with precision the rate of concentration of solid particles in the machining fluid such as to maintain a maximum machining efficiency. Several methods have already been suggested for measuring and controlling the pollution of the fluid used for electrical discharge machining, for example by measuring the light absorption of the fluid by optical means. However, such methods are not very precise and are poorly suited to measure the small concentrations of solid particles which are rather common during electrical discharge machining.